(a) Field of the Invention
The present invention relates to an amorphous alloy powder core having excellent high frequency properties and a nano-crystal alloy powder core with excellent soft-magnetic properties in the high frequency band range, and also relates to methods of manufacturing the same. More specifically, the present invention relates to a method of manufacturing an amorphous alloy powder core with good high frequency properties that can be made by low-temperature compression molding, by using a small amount of a polyimide resin or a phenolic resin binder with a crystalline magnetic core material, with the further benefit that the production yield is enhanced. The present invention also relates to a method of manufacturing a nano-crystal alloy powder core with excellent saturated magnetic flux density and effective permeability by performing a heat treatment of an amorphous alloy powder or an amorphous alloy powder core at a temperature greater than the crystallization temperature of the alloy.
(b) Description of the Related Art
Generally, amorphous soft-magnetic alloys exhibit excellent corrosion resistance and abrasion resistance, as well as strength and permeability, and are used as magnetic materials for electric and electronic appliances. They can be applied to transformers, inductors, motors, generators, relays, etc. Such amorphous soft-magnetic alloys are quenched during manufacture in order to maintain the amorphous state, and are generally formed in the shape of thin bands or fine lines. To manufacture a core of a particular shape, the amorphous soft-magnetic alloy used to form the shape is first ground to powder and is then compressed under a given pressure at a given temperature.
The bulk molding of the amorphous soft-magnetic alloy powder should be carried out at a temperature lower than the crystallization point for the alloy so as to maintain its amorphous state. However, since it is impossible to bulk mold the alloy powder at such a temperature, a method of binding the amorphous soft-magnetic alloy powder has been employed, in which a glass powder with a lower vitrification point than that of the amorphous soft-magnetic alloy powder was added by means of a ball mill, after which the resulting powder was softened and pressed at a temperature of about 500xc2x0 C. Hot isostatic pressing (HIP), and a hot press, etc. are generally used for the above method. There are other methods such as an explosive method, and an impact gun method, however special equipment is necessary to attain very high energy and the practice of these methods is time consuming, thus lowering the production yield.
Bulk molding of crystalline soft-magnetic alloy powder is carried out at a high temperature and uses, eg. a water glass as a binder. This is because the alloy powders are amenable to plastic deformation and strongly hold together during pressing at pressures of over 15 ton/cm2, since the crystalline alloy is lower in strength than the amorphous alloy. This process causes fewer cracks and the heating treatment after molding can be conducted at a high temperature of about 800xc2x0 C. to bring about the diffusion of atoms and to thereby attain stronger bonds between particles.
On the other hand, if one were to perform high-pressure molding of an amorphous alloy powder that has very high strength and ductility compared to the crystalline material, and were to use water glass as a binder, numerous cracks would be produced in the core. In addition, since the heating treatment that is carried out at below 500xc2x0 C. does not bring about diffusion of atoms, the final core would be very low in strength and easily broken.
It is an object of the present invention to provide a method of manufacturing an amorphous alloy powder core with good high frequency properties that can be made through low-temperature compression molding by using a polyimide resin or a phenolic resin with higher viscosity than a conventional water glass as a binder, thereby reducing the amount of the required binder, and assuring a higher production yield than is achieved with hot isostatic pressing.
It is another object of the present invention to provide an amorphous alloy core having a high molding density and no surface cracks, and that exhibits a low dependence on frequencies and constant permeability even in the high frequency band range because of the improved insulative properties of the alloy core particles.
It is still another object of the present invention to provide a method of manufacturing a nano-crystal alloy powder core with excellent saturated magnetic flux density and enhanced effective permeability by heat treating an amorphous alloy powder at a temperature higher than the crystallization starting temperature of the alloy and by using a polyimide resin or a phenolic resin as a binder.
It is still another object of the present invention to provide a nano-crystal alloy powder core having a high molding density and no surface cracks, and showing a low dependence on frequencies and constant permeability even in the high frequency band range because of the improved insulative properties of the alloy core particles.
In order to achieve the above objects, the present invention provides a method of manufacturing an amorphous alloy core including the steps of mixing an amorphous alloy powder with a solution made by dissolving a polyimide/phenolic resin binder in an organic solvent, evenly coating the surface of the alloy powder with the binder in liquid phase to make composite particles, molding the composite particles, and performing a heat treatment thereon.
Preferably, the above method may further include the steps of heat treating the amorphous alloy powder at a temperature of less than 500xc2x0 C. before mixing the amorphous alloy powder in the solution made by dissolving the polyimide resin or phenolic resin in the organic solvent.
Molding may be performed at a temperature of less than 200xc2x0 C. and under a pressure of 10 to 50 ton/cm2. The heat treatment is performed at 150 to 500xc2x0 C.
The amorphous alloy core has a saturated magnetic flux density of more than 0.80T and a permeability of more than 0.90, measured in 1 MHz and 0.1 MHz.
According to another aspect of the present invention, a method of manufacturing a nano-crystal alloy core includes the steps of mixing an amorphous alloy powder with a solution made by solving a polyimide/phenolic resin binder in an organic solvent, evenly coating the surface of the alloy powder with the binder in liquid phase to form composite particles, molding the composite particles at a normal temperature. and performing a heating treatment thereon at a temperature that is higher than the crystallization starting temperature of the alloy.
According to still another aspect of the present invention, a method of manufacturing a nano-crystal alloy core includes the steps of heat treating an amorphous alloy powder at a temperature of over its crystallization starting temperature to form a nano-crystal phase, mixing a solution made by dissolving a polyimide/phenolic resin binder in an organic solvent therewith, evenly coating the surface of the alloy powder with the binder in liquid phase to make composite particles, and molding the composite particles at 100 to 300xc2x0 C. The molding is performed under a pressure of 10 to 50 ton/cm2 for less than 1 minute.
The resulting nano-crystal alloy core has a saturated magnetic flux density of more than 1.10T and a permeability of more than 0.90, as measured at 1 MHz and 0.1 MHz. The properties of the nano-crystal alloy core of the invention are enhanced by more than 20% compared to the amorphous alloy powder core of the same composition prepared by conventional methods.